[PATCH 5/8] powerpc/pseries: Introduce helpers to gatekeep DTLB usage

[Naveen N. Rao]

Since we would be introducing a new user of the DTL buffer in a
subsequent patch, add helpers to gatekeep use of the DTL buffer. The
current usage of the DTL buffer from debugfs is at a per-cpu level
(corresponding to the cpu debugfs file that is opened). Subsequently, we
will have users enabling/accessing DTLB for all online cpus. These
helpers allow any number of per-cpu users, or a single global user
exclusively.

Signed-off-by: Naveen N. Rao <naveen.n....@linux.vnet.ibm.com>
---
 arch/powerpc/include/asm/plpar_wrappers.h |  2 ++
 arch/powerpc/platforms/pseries/dtl.c      | 10 ++++++-
 arch/powerpc/platforms/pseries/lpar.c     | 36 +++++++++++++++++++++++
 3 files changed, 47 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/plpar_wrappers.h 
b/arch/powerpc/include/asm/plpar_wrappers.h
index d08feb1bc2bd..ab7dd454b6eb 100644
--- a/arch/powerpc/include/asm/plpar_wrappers.h
+++ b/arch/powerpc/include/asm/plpar_wrappers.h
@@ -88,6 +88,8 @@ static inline long register_dtl(unsigned long cpu, unsigned 
long vpa)
        return vpa_call(H_VPA_REG_DTL, cpu, vpa);
 }
 
+extern bool register_dtl_buffer_access(bool global);
+extern void unregister_dtl_buffer_access(bool global);
 extern void register_dtl_buffer(int cpu);
 extern void alloc_dtl_buffers(void);
 extern void vpa_init(int cpu);
diff --git a/arch/powerpc/platforms/pseries/dtl.c 
b/arch/powerpc/platforms/pseries/dtl.c
index fb05804adb2f..dd28296c9903 100644
--- a/arch/powerpc/platforms/pseries/dtl.c
+++ b/arch/powerpc/platforms/pseries/dtl.c
@@ -193,11 +193,15 @@ static int dtl_enable(struct dtl *dtl)
        if (dtl->buf)
                return -EBUSY;
 
+       if (register_dtl_buffer_access(false))
+               return -EBUSY;
+
        n_entries = dtl_buf_entries;
        buf = kmem_cache_alloc_node(dtl_cache, GFP_KERNEL, 
cpu_to_node(dtl->cpu));
        if (!buf) {
                printk(KERN_WARNING "%s: buffer alloc failed for cpu %d\n",
                                __func__, dtl->cpu);
+               unregister_dtl_buffer_access(false);
                return -ENOMEM;
        }
 
@@ -214,8 +218,11 @@ static int dtl_enable(struct dtl *dtl)
        }
        spin_unlock(&dtl->lock);
 
-       if (rc)
+       if (rc) {
+               unregister_dtl_buffer_access(false);
                kmem_cache_free(dtl_cache, buf);
+       }
+
        return rc;
 }
 
@@ -227,6 +234,7 @@ static void dtl_disable(struct dtl *dtl)
        dtl->buf = NULL;
        dtl->buf_entries = 0;
        spin_unlock(&dtl->lock);
+       unregister_dtl_buffer_access(false);
 }
 
 /* file interface */
diff --git a/arch/powerpc/platforms/pseries/lpar.c 
b/arch/powerpc/platforms/pseries/lpar.c
index 3375ca8cefb5..6af5a2a11deb 100644
--- a/arch/powerpc/platforms/pseries/lpar.c
+++ b/arch/powerpc/platforms/pseries/lpar.c
@@ -65,6 +65,42 @@ EXPORT_SYMBOL(plpar_hcall);
 EXPORT_SYMBOL(plpar_hcall9);
 EXPORT_SYMBOL(plpar_hcall_norets);
 
+static DEFINE_SPINLOCK(dtl_buffer_refctr_lock);
+static unsigned int dtl_buffer_global_refctr, dtl_buffer_percpu_refctr;
+
+bool register_dtl_buffer_access(bool global)
+{
+       int rc = 0;
+
+       spin_lock(&dtl_buffer_refctr_lock);
+
+       if ((global && (dtl_buffer_global_refctr || dtl_buffer_percpu_refctr))
+                       || (!global && dtl_buffer_global_refctr)) {
+               rc = -1;
+       } else {
+               if (global)
+                       dtl_buffer_global_refctr++;
+               else
+                       dtl_buffer_percpu_refctr++;
+       }
+
+       spin_unlock(&dtl_buffer_refctr_lock);
+
+       return rc;
+}
+
+void unregister_dtl_buffer_access(bool global)
+{
+       spin_lock(&dtl_buffer_refctr_lock);
+
+       if (global)
+               dtl_buffer_global_refctr--;
+       else
+               dtl_buffer_percpu_refctr--;
+
+       spin_unlock(&dtl_buffer_refctr_lock);
+}
+
 void alloc_dtl_buffers(void)
 {
        int cpu;
-- 
2.21.0